A conventional diode used in a signal output device of a vehicle-mounted network has been known. Such a diode includes a p-type semiconductor substrate, an n-type semiconductor layer formed on the p-type semiconductor substrate, p-type isolation regions formed to surround a certain region of the n-type semiconductor layer on the p-type semiconductor substrate, an n-type buried layer formed across the p-type semiconductor substrate and the n-type semiconductor layer within the certain region, an n-type collector wall formed on the-type semiconductor layer and standing on a peripheral edge of an upper surface of the n-type buried layer toward a surface of the n-type semiconductor layer, and a p-type anode region and an n-type cathode region formed in a diode formation region within a region surrounded by the n-type collector wall of a surface layer of the n-type semiconductor layer.
In the foregoing conventional diode, a longitudinal PNP parasitic transistor is formed by an n-type semiconductor including the p-type anode region to which an anode is connected, the p-type semiconductor substrate, and the n-type buried layer between the p-type anode region and the p-type semiconductor substrate. In addition, a transverse PNP parasitic transistor is formed by an n-type semiconductor including the p-type anode region to which the anode is connected, the p-type isolation region, and the collector wall between the p-type anode region and the p-type isolation region. Since a current path is formed by such parasitic transistors, a leakage current flows in the p-type semiconductor substrate.